1. Field
Example embodiments of the inventive concepts generally relate to semiconductor memory devices and, more particularly, to memory devices with three-dimensional structure and program methods thereof.
2. Description of the Related Art
Semiconductor memory devices may be classified into volatile memory devices such as DRAM and SRAM and non-volatile memory devices such as EEPROM, FRAM, PRAM, MRAM, and flash memory. Volatile memory devices lose their stored data when their power supplies are interrupted, while nonvolatile memory devices retain their stored data even when their power supplies are interrupted. In particular, flash memory devices have advantages such as high program speed, low power consumption, and large data storage capacity. Therefore, a flash memory system including a flash memory is widely used as a data storage medium.
Flash memory devices are increasing in integration density to meet users' demands for better performance and lower costs. However, conventional two-dimensional flash memory devices are limited with respect to increasing integration density due to their fabrication processes. Three-dimensional flash memory devices have been proposed to overcome the limitation. A three-dimensional flash memory device is fabricated by vertically and horizontally stacking various layers and forming a channel hole. However, it is considerably difficult to form a uniform channel hole of a three-dimensional flash memory device. If a cross section of a channel hole of a three-dimensional flash memory device is not uniform, rising slope of a wordline voltage may vary between different wordlines.